Refer to FIG. 6 of the present application, which shows the structure of a prior art switch of the type that the present invention is concerned. The switch comprises a base 90 to receive a first electric wire 920 connected to a power source (not shown), a second electric wire 930 directly connected to an electric appliance (not shown), for example, an electric fan, a third electric wire 940 also connected to the electric appliance but via a diode 95, and a rotor 91 (which is formed of an insulating material) rotatably mounted on the base and drivable by a knob (not shown) connected thereto. Three contacts 910 are respectively received in recesses defined in a periphery of the rotor 91 to rotate therewith, wherein each of the contacts is electrically connected with each other. A first, second and third leaf spring 92, 93 and 94 are mounted on the base 90 to respectively connect with the first, second and third electric wires 920, 930 and 940 and extend toward the rotor 91. As shown in FIG. 6, when the rotor 91 is at this position, the wire 920 is simultaneously electrically connected with the wires 930 and 940 through the contacts 910; in this case, due to the impedance of the diode 95, most of the electric current from the wire 920 is introduced into the appliance through the wire 930. As the rotor 91 is rotated clockwise for 1/4 turn from the shown position, the leaf spring 94 becomes separated from the contacts 910; therefore, the electric current from the wire 920 is totally introduced into the appliance through the wire 930. As the rotor 91 is further rotated clockwise for 1/4 turn, the leaf spring 93 becomes separated from the contacts 910; therefore, the electric current from the wire 920 is solely introduced into the appliance through the wire 940 and the diode 95. Due to the impedance of the diode 95, the amount of voltage across the appliance at this point is reduced to a significant level in comparison with the above two cases, whereby the appliance can have a smaller output (for example, if the appliance is an electric fan, it may have a lower speed of rotation.) Finally, when the rotor 91 is further rotated for 1/4 turn, the wire 920 is separated from the contacts 910; thus, no current will flow into the appliance. At this point the knob indicates "Off".
Although the prior art switch has four controlling positions (including the "Off" position), its first position (as shown by FIG. 6) and the following position cause substantially the same amount of current introduced into the appliance, which, in turn, causes the appliance to have substantially the same level of output at these two positions. Therefore, one of the two controlling positions is superfluous.
Secondly, since the prior art switch is rotated to adjust the output of the appliance from a large output to a small output, this is disadvantageous from the view of energy conservation.
Thirdly, since the diode of the prior art switch is mounted outside of the base, the structure of the prior art switch cannot achieve a compact fashion.